In rock drilling, a drilling tool is used that is connected to a rock-drilling device via one or more drill string components. The drilling can be carried out in several ways, a common method being percussive drilling where an impulse-generating device, a striking tool, is used to generate impacts by means of an impact piston that moves forward and backward. The impact piston strikes the drill string, usually via a drill shank, in order to transfer impact pulses to the drilling tool via the drill string, and then on to the rock to deliver the energy of the shock wave. The impact piston is typically driven hydraulically or pneumatically, but can also be driven by other means, such as by electricity or some form of combustion.
Impulse-generating devices in which the shock wave is generated by an impact piston have the problem that the forward and backward movement of the impact piston results in dynamic acceleration forces that have an adverse effect on the impulse-generating device (the striking tool), and thereby the whole rock-drilling device. In percussive drilling, a feed force is used to press the rock-drilling device, and thereby the drill string and drilling tool, against the rock in front of it, in order to avoid the harmful reflections that can arise if the drilling tool is not in contact with the rock at the time of the impact. An impact piston that is accelerated in the direction of the impact gives rise, however, to counter forces in the opposite direction that act to move the rock-drilling equipment in a backward direction, away from the rock. These opposing forces mean that an increased feed pressure is required and that the drilling equipment must therefore be dimensioned for these larger forces, with the result that equipment is obtained that is larger and more expensive overall than is required by the actual shock wave energy.
In an attempt to reduce the problem of the acceleration forces of the impact piston, impulse-generating devices have been produced in which the shock wave energy is not transferred by a piston that moves forward and backward, but instead by pre-loading an impact element by means of a counter-pressure chamber, whereby pressure impulses are transferred to the drill string by means of the impact element by a sudden reduction in the pressure in the counter-pressure chamber.
According to the currently known technology, this solution generates shock waves with lower energy, and, in order to maintain the efficiency of the drilling, the lower energy in each shock wave is compensated for by the shock waves being generated at a higher frequency.
A remaining problem with the abovementioned striking tool that does not have an impact piston is, however, that a part of the impact energy is reflected and returned to the impulse-generating device as harmful energy.